(1) Field of the Invention
This invention relates broadly to a novel ampoule adapted to contain a liquid local anaesthetic and to a novel method for administering such anaesthetic.
More specifically, the apparatus of this invention relates to a novel ampoule adapted to contain an acidified liquid local anaesthetic and adapted to be placed in a standard hypodermic syringe prior to administration of the anaesthetic, which ampoule is compartmented to provide a proximal compartment for the liquid local anaesthetic adjacent the proximal end of the ampoule and a distal compartment for a liquid neutralizing agent adjacent the distal end of the ampoule.
More specifically, the method of this invention relates to the administration of an acidified liquid local anaesthetic through a body of alkaline liquid neutralizing reagent and thence into the tissues of a patient.
(2) Description of the Prior Art
The administration of local anaesthetics is a well-known procedure in the practice of medicine and dentistry.
The administration of a local anaesthetic typically involves the use of an ampoule, which may be of glass, containing the liquid local anaesthetic. The ampoule, immediately prior to use, is placed in the barrel of a conventional hypodermic syringe having a hand-operated plunger at the proximal end thereof and a hollow hypodermic needle at the distal end thereof, the proximal end of the hollow hypodermic needle extending partially into the barrel of the syringe. The proximal end of the ampoule is closed by a rubber stopper slidably fitted within the ampoule. The distal end of the ampoule is closed by a rubber diaphragm. In administering the local anaesthetic, the operator manually advances the ampoule in the barrel toward the distal end of the hypodermic syringe, thereby to cause the proximal end of the hypodermic needle, which extends into the barrel of the syringe, to perforate the rubber diaphragm at the distal end of the ampoule and communicate with the interior of the ampoule. Thereafter, the operator advances the plunger of the syringe against the rubber stopper of the ampoule, forcing the rubber stopper into the ampoule. The rubber stopper functions as a piston, forcing the local anaesthetic out of the distal end of the ampoule, through the hollow hypodermic needle and into the tissues of the patient.
Ampoules of the type described are well-known, one being an ampoule manufactured by Cook-Waite Laboratories, Inc. and sold under their registered trademark CARPULE.
Certain local anaesthetics, particularly used in the practice of dentistry, have relatively short shelf lives if they are alkaline, i.e., having a pH greater than 7.0. If these anaesthetics are acidified, their shelf lives can be increased substantially. Local anaesthetics such as lidocaine and mepivacaine are generally marketed as lidocaine and mepivacaine hydrochloride, respectively, with a pH as low as 5.0, meaning that they are quite acidic, and these acidified local anaesthetics have shelf lives of three to four years.
However, the administration of an acidified local anaesthetic causes a substantial amount of discomfort, and indeed pain, particularly in infiltrative local anaesthesia as employed in dentistry. It is known that very slow infiltration of the acidified local anaesthetic can reduce the pain associated with infiltration. It is a fact of life that demands on a dentist's time may preclude a very slow infiltration of local anaesthetic, especially with children, who frequently are agitated and fearful.
A partial solution to this problem has recently been devised. A sterile hypodermic needle was inserted into one end of an ampoule containing acidified liquid local anaesthetic and a portion of such anaesthetic was removed from the ampoule. A sterile hypodermic needle was then used to inject, through one end of the ampoule, a quantity of alkaline reagent. The quantity of alkaline reagent so injected into the ampoule, and its concentration, were sufficient to bring the pH of the mixture, after the ampoule was shaken to mix the two solutions, to above 7.0. Specifically, 0.18 ml. of anaesthetic solution such a 2% lidocaine hydrochloride (1/10 the volume of a 1.8 ml. ampoule) were replaced with 0.18 ml. of 8.4% sodium bicarbonate. The mixed solution was then administered to 50 patients, only 5 of whom said the injection hurt, only 15 of whom said the injection stung (most saying the sting was very little), 36 of whom said this procedure was more comfortable than previous procedures with acidified local anaesthetic, and 38 of whom reported that the injection was painless or they felt nothing. Clearly, neutralization of acidified local anaesthetic dramatically decreased the pain and discomfort normally associated with infiltration.
This partial solution, while effective, had certain shortcomings. Any time that sterile liquids are removed from an ampoule or injected into an ampoule, there is a risk of contamination, and therefore the partial solution mandated the application of most rigorous measures to assure sterility. Because the acidity of the local anaesthetic was neutralized, its shelf life was markedly reduced, and therefore the mixture of acidified local anaesthetic and neutralizing alkaline reagent could not be made up much in advance of its use.
It is known to provide a glass vial having a necked-down portion intermediate the ends thereof with a rubber stopper seated in the necked-down portion to define a first compartment adapted to contain a liquid and a second compartment adapted to contain a powder. A rubber diaphragm seals the open end of the vial. In use, the rubber diaphragm is pushed inwardly to pressurize the liquid in the first compartment and dislodge the rubber stopper from the necked-down portion of the vial. The vial is then shaken to mix the liquid and the powder so as to dissolve the powder. Thereafter, the needle of a hypodermic syringe is advanced through the rubber diaphragm into the vial and the solution in the vial is withdrawn for subsequent injection into the tissues of a patient. This vial, used by The Upjohn Company of Kalamazoo, Mich., is not an ampoule, does not solve the problems to which the present invention is directed, and does not function as an ampoule, particularly of the type herein disclosed and claimed.